1. Field of the Invention
The present invention relates generally to the field of chemical reactor vessels and more specifically to a reactor vessel provided with a system for automatically preventing runaway of exothermic reactions.
2. Description of the Prior Art
Throughout the chemical industry there are a wide variety of exothermic reactions which take place in closed reactor vessels. A number of conditions can lead to a runaway reaction and uncontrolled self-heating pressure build-up in the vessel. Examples of such conditions include loss of cooling or refrigeration, contamination of the reactor contents and overfilling with a critical reagent due to faulty instrumentation or human error.
To accommodate the potential for the runaway reaction, reactor vessels of the prior art are provided with some type of emergency relief system which must operate when a threshold pressure is reached. Typically the reactor is provided with a substantial vent line which exhausts into a fluid filled quenching tank through a quencher arm which is designed specifically for the reactor vessel and reaction involved. In the overpressure condition of a runaway reaction a rupture disc releases the flashing flow through the vent line to the quenching tank. The required size of the vent line is strongly dependent upon the selected upset condition and the self-heat or energy release rate of the particular reaction which is generally not known. Sophisticated analysis and research are therefore required to even approximate a proper design.
When the relief vents of the prior art open a frothy mixture of liquid and gas is discharged which in the extreme may involve the entire contents of the reactor vessel. As a result, for a given size relief vent, liquid being discharged fills a portion of the vent and effectively reduces the cross-section available for the venting of vapor. Because less vapor than was initially assumed can be vented per unit time, the pressure in the reactor vessel can continue to rise, potentially above the design limits. Further, because of this two phase flow, the mass of material being discharged is substantially greater than would be assumed for an all vapor flow. These factors in turn require large, elaborate and expensive receiving systems which are ineffective for low vapor pressure systems. Also for high vapor pressure systems, the self-heat rate corresponding to relief set pressure becomes very large relative to process conditions.